The invention relates to a refiner comprising a stator and a rotor, the stator and the rotor comprising a planar portion and a conical portion after the planar portion, the planar portion and the conical portion comprising refining surfaces provided with blade bars and blade grooves therebetween, and the planar portions of the refining surfaces of the stator and the rotor comprising at least two refining zones in the direction of the radius (R) of the planar portion.
The invention further relates to a blade segment of a refining surface of a refiner, which blade segment is configurable to form at least part of the refining surface of the stator or the rotor of the refiner and which comprises blade bars and blade grooves therebetween, which together form the refining surface of the blade segment, and which blade segment is provided with at least two refining zones in the direction of the radius of the refining surface.
Refiners for processing fibrous material typically comprise two, but possibly also more, oppositely situated refining surfaces, at least one of which is arranged to rotate about a shaft such that the refining surfaces turn with respect to one another. The refining surfaces of the refiner, i.e. its blade surfaces or the blade set, typically consist of protrusions, i.e. blade bars, provided in the refining surface and blade grooves between the blade bars. Hereinafter, blade bars may also be referred to as bars and blade grooves as grooves. The refining surface consists of a plural number of juxtaposed blade segments, in which case the refining surfaces of individual blade segments together form an integral, uniform refining surface.
WO 97/18307 discloses a refiner provided with a stator, i.e. a fixed, immobile refiner element, and a refiner element to be rotated by means of a shaft, i.e. a rotor. Both the stator with its refining surface and the rotor with its refining surface are formed of a planar portion substantially perpendicular to the rotor shaft and a conical portion provided after this planar portion and arranged at an angle to the planar portion. The planar and conical portions of the stator and the rotor are spaced apart such that a blade gap is formed between the refining surface of the stator and the refining surface of the rotor. The fibrous material to be refined is fed into the blade gap between the planar portions of the stator and the rotor. As the material to be refined is being processed, it moves forward in the blade gap into the blade gap between the conical portions of the stator and the rotor and finally away from the blade gap.
A problem with the refiner type disclosed in WO 97/18307 is the turning point formed by the planar portion and the conical portion, because already the change it causes in the direction of travel of the material to be refined complicates the feeding of the material to be refined from the planar portion to the conical portion. This harmful effect is further aggravated by the fact that also the point of inversion and the high pressure of steam created in the refining process set in this same area. The fibres therefore remain long at this location and get accumulated there, which in turn leads to high energy consumption and high pressure, which tends to open the refiner blades and thereby cause additional stress on the refiner structure.